Genetics influences evolution of tonal languages

A new report suggests that our use of tone to convey linguistic meaning may be …

Among the many ways you can define language differences, one of the easiest is by the use of tone. For some languages (like English), the differences between words that are pronounced similarly has to be figured out by context. In others, notably Chinese, different words can have a similar pronunciation but differ in tone. In the latest issue of PNAS, two authors argue that the use of languages that rely on tones may have a genetic component.

The authors must have been following the evolutionary literature, as they noted some reports on the genes ASPM and Microcephalin that suggested they were under evolutionary pressure in modern human populations and are undergoing selective sweeps. They were struck by the fact that the geographic distribution of some of the alleles of these genes lined up quite well with the distribution of tonal languages. So, they built a database that included information on the presence of nearly 1,000 alleles of these genes and linked it in to one which contained information on the distribution of 26 different linguistic features.

With that much information, a certain amount of correlation would be expected to be distributed at random. Instead, over 98 percent of the correlation was between specific ASPM and Microcephalin alleles and tone. The correlation withstood every statistical test they threw at it and remained after they controlled for the historic relationships among languages. All the data suggests that the use of tonal languages is influenced by genetics.

The authors interpret this information cautiously. Genetics is not the ultimate determinant of language use, as the authors note that under the right circumstances, pretty much anyone can learn any language. They actually suggest that these genetic influences, which are under evolutionary pressure themselves, influence the evolution of language. Instead of forcing an either/or use of tone, they cause populations that don't handle tone well to gradually decrease its use. Only over time do these gradual changes produce a stark, tonal/atonal distinction.

It was somewhat amusing how well a model biological evolution made for the evolution of language. The authors even note what might be called "transitional species" of language, such as Swedish and Japanese, which apparently have a limited form of tonality.